Yeast Enolase: To characterize the metal binding sites of this enzyme we are studying the Cobalt and chromous ion activated enzyme using U.V. and visible spectroscopy, rates and products of in situ metal oxidation, and ESR measurements. The resistance of the Cobalt enzyme to inactivation by H202 is being investigated to see if the metal site is shielded from H202 or if the CoII state is highly stabilized against oxidation. Red Blood Cell Pyruvate Kinase: The reversible oxidation of this enzyme appears to offer a control mechanism critical to the function of this cell. The factors that determine the rate of oxidation and reduction of the enzyme are being studied. The factors include the concentrations of PEP, FDP, ATP and metal ions.